Ideas for Adding Batteries to Existing Solar System

We have a 6.6KW system that is connected to the grid. I want to add the option to go off-grid, yet stay connected to the network - ie a switch that will allow for either.
I like the concept of redundancy and this also gives me the option to disconnect from the network if need be.

Anything I should consider with doing this? How much would it cost to have an installer hook up a basic (very small) battery bank to an existing solar setup.


  • gives me the option to disconnect from the network if need be.

    Can you elaborate further what you trying to achieve?

    Physical disconnection?

    Stop paying retailers supply charges?

    It is not clear what you meant.

  • +5

    Get a system that is automatic. You don’t want to have to turn the battery on and off constantly to make the best use of it.

    It’s not worth it unless you get a decent battery bank.

    I looked at it recently and it’s still a bit too expensive to be financially beneficial, but good environmentally.

  • You will need a hybrid inverter. Can make your own battery bank in the size you want with lifepo cells. You'll need a BMS. If you can't do anything yourself, this will not be cheap.

  • +1

    What Brendanm said.

    If your existing inverter is a hybrid inverter then you should be able to plug a battery directly into it and feed into it, although only the minority of inverters do this at this stage, my inverter installed earlier this year is a Growatt and luckily it can accept a battery feed in/out.

    If it's not a hybrid inverter you'll have to replace both the inverter and buy a new battery which can cost a fair bit (at this point it's not overly economically viable - with payback periods of 7-15 years depending on the size of the battery.)

    If cost isn't an issue and you're more about convenience and being off grid then go for it.

    • Would this also work for microinverters?

      • +1

        Probably not. The inverter system need to include taking solar sparks and jamming them into the house, giving leftovers to the grid and also converting battery sparks back to house sparks. It’ll also need to have some way of stuffing the ballad sparks into the battery - which doesn’t need an inverter.

  • Keep in mind for example a 5kw battery will supply, that, at best over a longer period of time, that is say 1kw per hour for 5 hours. If you drain it too fast it, it can affect the batteries life.

    You need to research this aspect based on your own projected needs when the solar isnt available. You might be surprised how much battery power you need for sustained use off grid.

  • We've just been through this in South Australia. It's been bitter sweet;

    As mentioned you will need a hybrid inverter.

    Here in SA if you are within reach of transmission lines, irrespective of whether connected to the grid, you will be charged daily service fees. You'll need to check with your local grid manager. The retail cartel has us by the short and curlies. There is no escape

    We installed 10kWh storage, supplied by 4kWh solar PVC. Now wish we'd opted for 20kWh because most days the battery is charged before noon and the majority of solar generation is being fed to the grid for a pittance. That said, on results so far, coming out of winter, at 6c FiT, soon to be 4c I am told, we should complete a full year pretty much cost neutral.

    NB: Be wary of high FiT offers; they are usually capped.

    IMO unless you are distant from the transmission lines you probably shouldn't go off grid. Instead, join a lobby group to get a better deal for hapless consumers and domestic generators.

    Oh, and DO NOT TRUST those selling you a system. Read the fine print. Get an inclusive fixed price contract. Make sure that you are dealing with a well established company that takes responsibility for supply & installation. We got caught like this and are currently being buck passed between hardware supplier and the sub contractor who did the installation over an issue that's cropped up. The matter is now with a government department here in SA.

    There, I feel better now.

  • It's possible using hybrid solar system, and hence right now, majority of the homeowners are tapping the utility grid for electricity and energy storage is significantly cheaper.